1. Field of the Invention
The present invention relates to an image acquisition apparatus and a control method therefor. More particularly, the present invention relates to an image acquisition apparatus including an interference optical system, which is used for, for example, ophthalmologic diagnosis and treatment, and also relates to a control method therefor.
2. Description of the Related Art
Major examples of the currently-available ophthalmologic apparatuses which employ optical instruments include a confocal scanning laser ophthalmoscope (SLO) and an optical coherence tomography (OCT) apparatus (hereinbelow, referred to as OCT apparatus).
The OCT apparatus measures the state of a fundus with high sensitivity with the use of an interference beam obtained by irradiating a sample with a low coherence beam and then causing interference between the beam reflected from the sample and a reference light. In addition, by scanning the sample with the low coherence beam, the OCT apparatus is capable of acquiring, with high resolution, a tomographic image of the retina in the fundus of an eye to be inspected.
In general, there is used a tomographic image of the retina which is acquired through so-called B-scan by the OCT apparatus. This image is acquired by executing scan in a depth direction (Z-direction) of the retina, called A-scan, multiple times in an X-direction. With the B-scan, the internal state of the retina can be observed as well in the same way as in the case of using images obtained by the conventional fundus cameras or the like. Thus, it is possible to observe lesions inside the retina, in particular, macular degeneration and a macular hole. By taking multiple images through the B-scan in a Y-direction, a 3D retinal image is acquired, and this image is favorably used for observing the extent of a lesion and each layer inside the retina, particularly, for observing the ganglionic layer of optic nerve, which suffers glaucoma.
By the way, the conventional resolution in a lateral direction has been about 10 μm, but the resolution needs to be made higher when a capillary aneurysm or a photoreceptor cell is desired to be observed at the early stage of diabetes, for example. In this case, when optical resolution in the lateral direction is made higher, it is impossible for a single focusing point to achieve an in-focus state in a longitudinal direction across an entire area. To address this, image taking needs to be performed by using a technique called zone focusing, in which multiple focusing points are used.
Japanese Patent Application Laid-Open No. 2007-101250 discloses a basic configuration of the zone focusing. However, in this case, a large amount of data is acquired, and thus the image taking takes several tens of seconds. Hence, it is essential to take measures against the blink which occurs during this period.
As a measure taken for the fundus camera against the blink, Japanese Patent Application Laid-Open No. H07-323011 discloses a configuration in which, when a blink has been detected during the image taking, it is judged that data acquired during this period is unusable, and the data is deleted.
When the above-mentioned zone focusing is employed to take a 3D retinal image having a size of 10 mm ×10 mm with a lateral resolution of 3 μm and with the number of zones of 3, the data amount becomes about 20 Gbytes.
As for the time period required for the image taking, by using a so-called multibeam method in which multiple light sources and multiple line sensors are used to simultaneously acquire images of multiple portions, the data can be acquired in 30 to 40 seconds.
Further, when such data is transmitted to a computer for display and storage, it takes 40 seconds or longer to transmit the data even with a USB 3.0, which is the latest general-purpose data bus. In this case, because a data rate for the image taking is higher than a data transmission rate for communication, a communication data buffer having a capacity of 20 Gbytes is simply required. The data also needs to be transmitted after the data acquisition, and hence the data transmission takes more time than the image taking.
Further, there is a problem that, due to the blink, the time period required for the image taking becomes 1.2 times or longer, and that the data amount also becomes 1.2 times or larger, that is, 24 Gbytes or larger.